Method and system for multi-layer network routing

ABSTRACT

Each node of a telecommunications network determines interface point connection type attributes available for each signal type supported by the node. Each signal type represents a different connection routing layer within the telecommunications network. Adaptation costs involved in traversing from one connection routing layer to another connection routing layer in the node are calculated. The connection type attributes and adaptation costs are included in a link state advertisement broadcasted by each node in the telecommunications network. A route calculation is performed for a desired signal to determine a route through the telecommunications network for the signal. The route calculation takes into account the various connection type attributes, availability, and adaptation costs in determining the shortest route for the signal through the telecommunications network.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit of U.S. Provisional Application No.60/661,203 filed Mar. 11, 2005.

This application is a continuation-in-part application of U.S.application Ser. No. 10/355,306 filed Jan. 31, 2003.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to telecommunications networkcontrol processing and more particularly to a method and system formulti-layer network routing.

BACKGROUND OF THE INVENTION

Calculation of a route through a network is based on link attributesadvertised by each node in the network. There are several known linkattributes that may be advertised by nodes 12 within telecommunicationsnetwork 10. These link attributes include traffic engineering metric,maximum or total reservable bandwidth, unreserved bandwidth, resourceclass/color, link protection type, and shared risk link group. Thetraffic engineering metric specifies the link metric for trafficengineering purposes. The maximum or total reservable bandwidthspecifies the maximum bandwidth that may be reserved on this link in onedirection. Unreserved bandwidth specifies the amount of bandwidth notyet reserved on the link in the one direction. Resource class/colorspecifies administrative group membership for this link. The linkprotection type specifies the protection capability that exists for thelink. The shared risk link group attribute identifies a set of linksthat share a resource whose failure may affect all links in the set.

The link state advertisement may also include an Interface SwitchingCapability Descriptor. The Interface Switching Capability Descriptordescribes the switching capability for an interface where the link isdefined as being connected to a node by an interface. For example, aninterface that connects a given link to a node may not be able to switchindividual packets but it may be able to switch channels within aSynchronous Optical Network (SONET) payload. Interfaces at each end of alink may not have the same switching capabilities. For bi-directionallinks, the switching capabilities of the link are defined to be the samein either direction for data entering and leaving the node through thatinterface. For a unidirectional link, it is assumed that the InterfaceSwitching Capability Descriptor at the far end of the link is the sameas at the near end of the link. A unidirectional link is required tohave the same interface switching capabilities at both ends of the link.

The Interface Switching Capability Descriptor may specify a switchingcapability, an encoding type, a maximum and minimum labeled switch path(LSP) bandwidth, and interface maximum transmission unit. The switchingcapability descriptor specifies whether the interface is layer 2,packet, time division multiplex, lambda, or fiber capable as well aswhether the interface supports more than one of these types. Maximum LSPbandwidth specifies the smaller of the unreserved bandwidth and themaximum reservable bandwidth per priority. Minimum LSP bandwidthspecifies the minimum amount of bandwidth that may be reserved. Theinterface maximum transmission unit descriptor defines the maximum sizeof a packet that can be transmitted on this interface without beingfragmented. Descriptors other than the switching capability descriptorare dependent on the type of switching capability defined in theswitching capability descriptor.

The link attributes and interface switching capability descriptordiscussed above are advertised by a node for its own egress interfaceonly and require route calculations to find the reverse advertisementfor a bi-directional link in order to determine the capabilities of aneighbor's end of the link. This unnecessarily complicates routecalculation and adds the limitation that unidirectional links must havethe same capabilities at both ends.

SUMMARY OF THE INVENTION

From the foregoing, it may be appreciated by those skilled in the artthat a need has arisen for a technique to provide link stateadvertisements in a telecommunications network in order to facilitatemulti-layer routing. In accordance with the present invention, a methodand system for multi-layer network routing are provided thatsubstantially eliminate or greatly reduce disadvantages and problemsassociated with conventional route calculation techniques.

According to an embodiment of the present invention, there is provided amethod for multi-layer network routing that includes establishing aninterface point at each node of a network and determining signal typesimplemented at each node of a network. Each signal type indicates aconnection routing layer in the network. Connection types through eachinterface point for each signal type and connection routing layer ofeach node of a network are determined for each link of each node. Anavailability of each connection type is also determined. The signaltypes, connection types, and availability are broadcast from each nodeto each neighboring node in the network. Using this broadcastedinformation, a route through the connection routing layers of thenetwork may be determined for each signal sent in the network.

The present invention provides various technical advantages overconventional data management techniques. Some of these technicaladvantages are shown and described in the description of the presentinvention. Embodiments of the present invention may enjoy some, all, ornone of these advantages. Other technical advantages may be readilyapparent to one skilled in the art from the following figures,description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present invention andfeatures and advantages thereof, reference is made to the followingdescription, taken in conjunction with the accompanying figures, whereinlike reference numerals represent like parts, in which:

FIG. 1 illustrates a simplified diagram of a telecommunications network;

FIG. 2 illustrates a simplified diagram of a multiple connection routinglayer configuration of the telecommunications network;

FIG. 3 illustrates connection type attributes determined and advertisedat each node in the telecommunications network;

FIGS. 4A-C illustrate an example link state advertisement generated ateach node;

FIGS. 5A-B illustrate a process flow for generating a route calculationimplementing the connection type attributes;

FIG. 6 illustrates an additional step involved in the generation ofcandidate nodes performed during the route calculation;

FIG. 7 illustrates an additional step involved in the generation ofcandidate nodes during the route calculation;

FIG. 8 illustrates a layer isolated connection routing approach to amulti-layer network;

FIG. 9 illustrates flexible connectivity within a node interfacerepresented by a connectivity block with interface points;

FIG. 10 illustrates connection type attributes determined according toan interface point at each node and advertised at each node in thetelecommunications network;

FIG. 11 illustrates an example of a signal stack representing thecurrent layers for the connection being routed at a node with aninterface point;

FIG. 12 illustrates an example of a candidate entry associated with acandidate node for placement into a candidate node list;

FIGS. 13A-B illustrate a process flow for generating a route calculationimplementing the connection type attributes for connectivity through aninterface point of a node;

FIG. 14 illustrates an additional step involved in the generation ofcandidate nodes having interface points performed during the routecalculation;

FIG. 15 illustrates an additional step involved in the generation ofcandidate nodes having interface points during the route calculation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simplified diagram of a telecommunications network 10.Telecommunications network 10 includes a plurality of switching pointsor nodes 12 interconnected by links 14. Each node 12 is operable totransfer telecommunications signals using one or more signal types.Examples of signal types include Digital Service Level 1 (DS1), DS3,Virtual Tributary Level 1.5 (VT1.5), Synchronous Transport Signal Level1 (STS-1), STS-3c, and Optical Carrier Level 3 (OC-3). Nodes 12 may alsosupport other conventional signal types readily known by those skilledin the art. Each signal type represents a different connection routinglayer within telecommunications network 10. For each signal carriedwithin telecommunications network 10, a route to its intendeddestination is determined. Determination of the route throughtelecommunications network 10 may be made at an originating node 12, anode 12 acting as a supervisory or control node, or at a centralizedmanagement node 16 according to a desired design for telecommunicationsnetwork 10. Determination of a route and generation of relatedinformation associated with nodes 12 of telecommunications network 10may be performed by appropriate processing modules.

To automatically provision a signal through telecommunications network10, a route is calculated and a connection setup is derived from thecalculated route for informing nodes 12. The route identifies theswitching equipment at nodes 12 and the appropriate links 14 that thesignal traverses in order to reach a destination node 12 from anoriginating node 12. Once the route has been calculated, signaling ofthe connection setup to the appropriate nodes 12 in telecommunicationsnetwork 10 is performed in order to establish the intermediate switchingconnections necessary to provide end to end service for the signal.Alternatively, the connections can be configured from a central sourceor by other means according to desired implementations. Signaling forthe connection setup is performed by standard techniques known by thoseskilled in the art.

FIG. 2 shows an example layered view of telecommunications network 10.Routing of transport network signals over telecommunications network 10may be accomplished by layer isolated connection routing or multi-layerconnection routing. A layer is an abstraction containing the switchingpoints and links that operate within one signal type. For the exampleshown in FIG. 2, layer 20 is associated with the DS1 signal type, layer22 is associated with the DS3 signal type, and layer 24 is associatedwith the STS-1 signal type. A client layer is considered to be theoriginally requested network layer and a server layer provides a trunkcapability for the client layer. Other layers may also be present withintelecommunications network 10 with one layer being present for eachsignal type supported by telecommunications network 10.

Layer isolated connection routing provides for a separate routinginstance to exist for each layer supported by telecommunications network10. These routing instances operate independently of each other. Thus,each layer is unaware of the potential connectivity available within theother layers. By not knowing the connectivity available within otherlayers, the client layer is not able to optimally determine a point torequest a server layer connection between two points in the clientlayer. In this manner, the client layer may pick non-optimal points forrequesting a server layer connection in order to complete the route atthe client layer. Moreover, the paths available at the server layer maynot meet certain service requirements. If the client layer is unable toidentify the characteristics of an available server layer connectivityin advance of making the request for a trunk connection, the clientlayer must wait for the route calculation to complete before determiningwhether the service requirements can be met. If the service requirementscannot be met, the client layer will need to reconsider the route it hastaken and attempt to find another route that allows the servicerequirements to be met. Though the server layer may provide a list ofconnection possibilities with their respective attributes to the clientlayer, developing a list of paths and attributes at the client layer foreach destination within the server layer would be processor and memoryintensive when a network has a high number of paths between endpoints inthe server layer and each path could have a different set of attributes.The present invention provides an embodiment to effectively use layerisolated connection routing in a multi-layer connection routingenvironment.

Multi-layer routing provides for a single routing instance to beresponsible for connection routing within multiple layers oftelecommunications network 10. This routing instance is able to view thestatus and attributes of all links within multiple layers and allows forbetter routes to be determined with fewer processor cycles and lessmemory. Conventional link advertisement is insufficient to support routecalculation involving adaptation to mapped and multiplexed server layersand does not allow for different costs to be assigned to linkconnections at different network layers on the same advertised link.There is typically not sufficient information to determine acceptableroutes in multi-layer networks unless all boundary nodes are capable ofswitching at all network layers, which may not be possible in a networkdesign. Also, current routing practices do not support routing throughpooled resources for adaptation and/or interworking functions and do notaddress all types of routing constraints that are necessary foreffective route calculation in multi-layer networks. The presentinvention provides an embodiment that turns these disadvantages intoadvantages for effectively providing multi-layer routing.

Routes are calculated through the use of an algorithm. A commonalgorithm used in the calculation of a route through a network is knownas Dijkstra's algorithm. Dijkstra's algorithm is a standard subroutinefor finding shortest paths from an originating node to a destinationnode taking into account different weights or costs involved intraversing through the network. A variation of Dijkstra's algorithm,referred to as extended Dijkstra's algorithm or Constrained ShortestPath First (CSPF) algorithm, takes into account a link's attributes,availability guarantees, and economic cost to use to determine if thelink can satisfy the routing constraints provided in a routing requestto a specified destination node. In this manner, geographic diversity ofa signal may be provided, economic cost for a connection may beminimized, or other desirable routing behaviors may be produced. Inorder to perform multi-layer network routing, each node determines linkstates and advertises these link states throughout telecommunicationsnetwork 10. At each layer supported by telecommunications network 10,each node advertises various attributes to neighboring nodes. These linkstate advertisements are used in performing the route calculations usingDijkstra's algorithm or other route determination techniques.

FIG. 3 shows connection type attributes that may be supported by a nodeand advertised to a neighboring node. These connection type attributesadd efficiency and flexibility to route calculations not available withconventional attribute advertisements. Connection type attributesinclude Transit 30, Source 31, Sink 32, Dangling Egress 34, DanglingIngress 35, Dangling Source 36, and Dangling Sink 37. Connection typeTransit 30 represents an ability of the advertising and neighbor node toreceive transport network signals from a node and forward the transportnetwork signals to the next node in the route. Connection type Source 31represents an ability of the advertising node to originate transportnetwork signals at the current layer and an ability for a neighbor nodeto forward the transport network signals to the next node in the route.Connection type Sink 32 represents the ability of the advertising nodeto forward the transport network signals to the neighbor node fortermination. Connection type Dangling Egress 34 represents the abilityof the advertising node to adapt transport network signals from thecurrent connection routing layer to a server connection routing layer.Connection type Dangling Ingress 35 represents an ability of a neighbornode to receive transport network signals at the current connectionrouting layer from a server connection routing layer. Connection typeDangling Source 36 represents an ability of an advertising node tooriginate transport network signals at the current connection routinglayer and adapt the originating transport network signals to a serverconnection routing layer. Connection type Dangling Sink 37 represents anability of a neighbor node to receive transport network signals at thecurrent connection routing layer from a server connection routing layerand terminate the current transport network signals.

At physical medium layers, dangling relationships are not possible sincethe medium is assumed to be connected to the neighbor node and physicalmedia are not subject to adaptation to other server layers. At physicalsignal layers, it is possible that equipment inserted into the physicallink between nodes has properties that are more restrictive than theswitching equipment at the ends of the link. For example, twotransparent cross-connects may be connected by a fiber span thatincludes a SONET repeater. This would limit the link to SONET clientswhile the switching equipment does not have this limitation. In thiscase, the limiting properties of the span may be projected into theswitches in a way that accurately indicates the type of connectivityavailable. The limitation is adopted by the nodes as a characteristic ofthe advertised link though the switching equipment themselves are notthe source of the limitation.

FIGS. 4A-C show an example of an advertisement performed by a node 12according to the present invention. In FIG. 4A, the attributesunreserved bandwidth and maximum LSP bandwidth are shown. Theseattributes may be advertised once per link. The conventional attributemaximum or total reservable bandwidth is not needed sinceoversubscription may be handled by simply adjusting the unreservedbandwidth attribute by an appropriate fraction of the bandwidthreservation for each link state protocol assigned to the link.

FIG. 4B shows a connectivity attribute group (CAG) which may beadvertised as needed. The CAG includes the signal type, the connectiontypes supported and available, server signal type availability andassociated adaptation cost, client signal type availability andassociated adaptation cost, and server endpoint affinity. Each nodedetermines the neighbor nodes with which it communicates during anidentification phase of operation. A capability exchange phase is thenperformed so that a node can learn the various capabilities of each ofits neighbor nodes. With this information, a node can build CAGs foreach link with each neighbor node. Alternatively, these phases may beprovisioned at node installation.

A CAG is formed and advertised for each signal type supported by thenode. The signal type identifies the layer for this link beingadvertised. The connection type identifies one or more of the connectiontypes shown in FIG. 3. The server signal type availability indicatesthat the node has the capability to adapt the current signal type to anidentified server layer and that source connectivity is available atthat server layer on this link. The adaptation cost identifies the costinvolved in extending the dangling egress connectivity in order totraverse to the identified server layer. The client signal typeavailability indicates that the neighbor node has the capability toadapt the current signal type to an identified client layer and thatdangling connectivity is available at the identified client layer onthis link. The adaptation cost identifies the cost involved in extendingthe sink connectivity in order to traverse to the identified clientlayer. The server affinity endpoint field identifies a list of routeridentifiers that indicate which nodes should have preferential treatmentfor termination of a server trail that originates at this node whilerouting this signal type.

The connection types and associated availability are shown as bit fieldswith one bit position for each connectivity type defined above. Thesefields indicate whether each connectivity is supported and currentlyavailable for this link. Though shown in this manner, the link stateadvertisement may take on any form as desired for the communication ofthis information. If a connection type is advertised as currentlyavailable for a link, this indicates that at least one link connectionof that type is available. To support setup of multiple co-routedconnections, the advertised information could be extended to include thenumber of available connections of each type. However, the benefit ofthis extension may not be worth the resulting increase in database sizeas crankback may be used to address the relatively rare cases in whichthe advertised information is not sufficient to guarantee that thecalculated route is acceptable.

FIG. 4C shows additional attributes that may be advertised for eachlink. These attributes may be repeated as needed before the CAG to whichthey apply. These attributes include resource class/color, linkprotection type, and shared risk link group. These attributes relate tovarious routing constraints. If they are not included, the defaultvalues apply. Any of these attributes may be individually repeated witha new value in order to set that value for the CAGs that follow.

FIGS. 5A-B show an example process in determining a route calculationusing the advertised CAG information. The process shows how Dijkstra'salgorithm is changed to utilize the CAG information to accomplish routeextension via multiplexed and mapped server trails. Though changes toDijkstra's algorithm are shown, such changes are shown for examplepurposes only as the advertised CAG information may be implemented inother link state based route determination techniques and not limited toapplication to Dijkstra's algorithm. In the process shown, each node hasan associated node identifier and a signal stack to uniquely identifythe node. The signal stack is a stack of signal types that represent thecurrent layers for the connection being routed at this node. As with allstacks, new values are added or pushed on the top of the stack andvalues are removed or popped from the top of the stack.

The calculation performed by the process of FIGS. 5A-B yields a set ofintra-area routes associated with an area, Area A. A shortest path treeis determined by a node calculating the route using a specified node inthe network topology as a root. The formation of the shortest path treeis performed in two stages. In the first stage, only links between nodesin a single client layer are considered. In the second stage, linkswithin one or more server layers are considered. At each iteration ofthe algorithm, there is a list of candidate nodes. Paths from the rootto these candidate nodes have been determined but the shortest pathshave yet to be defined. Paths to the candidate node that is closest tothe root are guaranteed to be shortest. A path is said to be shorter ifit has a smaller link state cost. The link state cost of a path is thesum of the costs of the path's constituent links as they exist in alayer network (i.e., CAG). Upon identification, a candidate node isadded to the shortest path tree and removed from the candidate nodelist. Nodes adjacent to the candidate node added to the shortest pathtree are examined for possible addition to the candidate node list andthe shortest path tree. The algorithm continues to reiterate until thecandidate node list is empty.

In FIGS. 5A-B, process flow begins at block 50 where the data structuresof the algorithm are initialized and candidate nodes are cleared. Ashortest path tree is initialized by adding first a node, for examplenode V, representing the root with a signal stack containing the signalrequested to be routed. Subsequently, the shortest path tree is updatedto include new nodes meeting the desired routing constraints. Area A'sTransit Capability is set to False. At block 52, the link stateadvertisement of node V added to the shortest path tree is examined.Each link described by the link state advertisement provides signaltypes and costs to neighboring nodes. For each described link beginningat block 54, if the attributes of the link between node V and aneighboring node, for example node W, do not satisfy the routingconstraints requested, the examined link is skipped and the next link isexamined. If routing constraints are satisfied, process flow proceeds toblock 56 where node W's link state advertisement is examined. At block57, if the link state advertisement for node W does not exist, hasreached a maximum age, or does not include a link back to node V, thenthe next link in Node V's link state advertisement is analyzed.Otherwise, process flow proceeds to block 58 for an analysis of each CAGin the link. At block 59, if the attributes of the CAG do not satisfythe routing constraints, the next CAG in the link is analyzed. Ifrouting constraints are satisfied here, process flow proceeds to block60 where the signal type of the CAG is compared to the top of node V'ssignal stack. If there is no match, the next CAG in the link isexamined.

Upon a match of a signal type, process flow proceeds to block 62 wherethe connection types of the CAG are examined in order to generate newcandidate nodes. If transit connectivity is available, an instance ofnode W is formed with the current signal stack to specify uniquenessfrom one instance of node W to another. The advertised cost of eachinstance is set to the transit cost for the CAG. If sink connectivity isavailable, the signal stack for node V has more than one entry, and anyclient signal type of the CAG matches the second signal type in thesignal stack of node V, an instance of node W is formed for sinkconnectivity with the current signal stack excluding the top element ofthe signal stack for uniqueness and the advertised cost is set to theCAG adaptation cost for that client signal type. If dangling egressconnectivity is available, an instance of node W is formed with thecurrent signal stack for dangling egress and for each server signal typein the CAG. The advertised cost is set to the CAG adaptation cost foreach server signal type. For each instance of node W generated, processflow proceeds to block 64 to determine if the newly generated instanceof node W is already on the shortest path tree. If so, move on to thenext generated instance of node W. If not, process flow proceeds toblock 66 where the link state cost for the path from the root to node Wis calculated. The link state cost is the sum of the link state cost ofthe shortest path to node V and the advertised cost. At block 68, if thelink state cost is greater than or equal to the value that alreadyappears for node W in the candidate node list, then the next CAG isexamined. If the link state cost is less than the value that appears fornode W on the candidate node list or if node W does not yet appear onthe candidate node list, then an entry in the candidate node list fornode W is set to the calculated link state cost at block 69 and the nextgenerated node W is examined.

Once all generated node W's for each CAG for each link have beenexamined, process flow proceeds to block 70 where a node in thecandidate node list that is closest to the root is chosen and added tothe shortest path tree. At block 72, if the node added to the shortestpath tree has a link state advertisement indicating that the destinationis directly connected or reachable and the signal stack for the addednode contains one entry equal to the destination signal requested, thenthe calculation of the route is complete. The route is obtained bytracing back from this added node to the root of the shortest path tree.If the route is not complete, process flow returns to block 52 toexamine the link state advertisement for the newly added node.

When determining a route of a sub-network connection for a signalthrough a network, it is desirable to traverse from a client layer,where the signal originates, to a server layer and return. However,while the destination node may be accessible through both client andserver layers, the destination node may not support the adaptationfunction needed to support the client signal on all of its interfaces atthe server layer. As a result, the route calculation develops a paththat uses an adaptation function to return the connection to theoriginating layer of the signal prior to completing the route. Thisbehavior is supported through the sink connection type. Since the sinkconnection type has an associated signal type, it is possible to requirethe sink connection type match the type of signal being routed. In thecase where a particular client signal type is not supported on aninterface, the constraint matching function will invalidate the sinkconnection as a candidate for completing the signal routing. The routecalculation will then continue to evaluate other candidates. Thisbehavior is also preferable when the destination node for which a routeis being calculated is not the terminating node but a border node whichconnects this route calculation domain to another domain. A link can beidentified as being a border by looking at the advertisement type foundin the supporting routing protocol.

When determining the route of a signal through telecommunicationsnetwork 10, adaptation functions advertised on a link become candidatesfor extending that route through a server layer. This candidate will beevaluated along with other candidates that are within the same layer asthe signal being routed. The cost of the adaptation function, oradaptation cost, becomes a determining factor as to when a server layerconnection will be necessary to complete the route for the signal. Theremay be times where it is desirable to control the points at which serverlayer extension will be allowed in route calculation. This does notchange the fact that an adaptation function exists and it is not removedfrom the advertisement described above. Instead, a special adaptationcost, such as 0xffff, can be used to denote that route extension througha server layer is prohibited for the signal.

FIG. 6 shows the change in the process of FIGS. 5A-B to implement thisspecial adaptation cost. Since the adaptation cost is listed as part ofthe CAG associated with traversing a signal from a client layer to aserver layer, the review of the adaptation cost occurs at the time thatthe adaptation is pushed onto the signal path. The availability of theadaptation also is checked when traversing from the server layer back tothe client layer. Consequently, the return from server layer to clientlayer imposes a reverse check on the availability of the client layer toserver layer adaptation function. If the reverse check fails during theroute calculation, then the return to the client layer cannot beaccomplished at this point and a new candidate will then be evaluated.The check for the special adaptation cost occurs during the generationof new candidate nodes. During the check for availability of a sink ordangling egress availability, if the adaptation cost has the specialadaptation cost value, in this case 0xffff, then a candidate node is notgenerated. If the adaptation cost is not the special adaptation costvalue, then a candidate node is added to the candidate node list.

FIG. 7 shows an example change to the process of FIGS. 5A-B implementingan affinity cost adjustment for route extensions via multiplexed servertrails. When extending a route through a dangling egress followed by aserver layer source connection, a special candidate route is createdthat has an added endpoint constraint that it must reach a matchingserver layer sink connection at a node that is already a neighbor of thecurrent node for the link containing transit connections at the clientlayer being routed. This special candidate route has its cost adjustedby reducing or eliminating the adaptation cost for the server layer. Theendpoint constraint is applied to this route candidate, and any routecandidates that are generated from it, as the route calculationproceeds. The endpoint constraint for the special candidate route isdetermined by identifying all the neighbors of the current node on linksthat support transit connection types at the layer being routedregardless of whether or not these links currently have transitconnections available. For the sink connectivity check of block 62, theadded limitation on generating a node W is that the top of the signalstack for node V has either a NULL endpoint constraint or the endpointconstraint includes node W. For the dangling egress connectivity check,a node W is generated with both an endpoint constraint and a NULLendpoint constraint. The advertised cost for the first generated node Wis set to the CAG transit cost and the advertised cost for the secondgenerated node W is set to the CAG adaptation cost. The endpointconstraint is a list of affinity endpoints that can be used to terminatethe server layer trail and achieve the costs associated with the path tonode V. Any signal in the signal stack, except the bottom signal, can beassociated with a unique endpoint constraint. This method could beextended to create special candidate routes with different costdiscounts depending on the number and size of existing trunks to eachcurrent neighbor node.

FIG. 8 shows the implementation of layer isolated connection routing ina multi-layer network. Through the effective advertisement and routecalculation described above, effective multi-layer network routing canbe achieved. However, there may situations where it may be beneficial toprovide layer isolated connection routing in a multi-layer network. Amain limitation of layer isolated connection routing discussed above isthe inability to take into consideration potential connectivity that canbe supplied by server layer connections through links to the clientlayer in which the signal is to be routed. This limitation can beeliminated by assigning a node identifier to a fictitious node, orpseudo node 80, that serves to represent the potential connectivityprovided by a server layer between switching equipment operating at theclient layer.

Typically, a node identifier is assigned to a network node. The nodeidentifier serves to correlate all the links advertised relative to thatnode as having a common switching point through which signals can berouted. In multi-layer networks, there may be resources that could beused to create additional connectivity or new links between nodes bycreating new trails in a server layer of the network. However, it wouldbe inefficient to advertise all possible new links due to the vastnumber of possibilities. Instead, the potential connectivity provided bya server layer can be effectively summarized through the pseudo node.The pseudo node provides the possibility that any node at the edge ofthe server layer may be connected to any other node. The pseudo noderepresents the potential server layer connectivity in support of theclient layer without the need to show the details of the server layerconnectivity.

For each client layer node connected to a server layer, one or morelinks would be included in the link state database to represent thisconnectivity. These links would be included in the link stateadvertisement of the node in the client layer. Route calculations couldthen take into account the possibility of creating new paths in theserver layer by traversing links to and from the pseudo node. The costof these links can be set according to the desired policy regarding thepreference that should be given to using existing links in the clientlayer versus the newly created links to the pseudo node using the serverlayer.

Advertisement of links from the pseudo node must also be made. Generallyeach node in the network advertises its outgoing links. However, thepseudo node is fictitious. To overcome this, the content of a linkadvertisement may be independent from its source. In distributedflooding protocols, the neighbor node from whom a node receives a linkadvertisement is often not the node originating that link advertisement.By exploiting this feature of flooding protocols, a client layer node isallowed to advertise a link from itself to the pseudo node and alsoadvertise the corresponding link from the pseudo node to itself. Thisadvertisement is created as if it was generated by the pseudo node andthen flooded throughout the network as any other link advertisement.This allows distributed network implementations to employ pseudo nodeswithout the added complexity of creating a separate pseudo node routingprotocol entity.

Though pseudo nodes have been used in the past, the present invention isable to apply pseudo nodes technique to multi-layer transport networks.Pseudo node information being advertised does not require designatedrouter election and other coordination between proxy advertisers. Theuse of pseudo nodes in a multi-layer network provides the ability tocontrol, via provisioning, the communities connected to a given pseudonode to effect routing policies. Also, an ability is provided for nodesadvertising connection to a pseudo node to recognize the pseudo node inroutes and request a connection through the core network to replacepseudo node hops in the route.

Another concept that may be implemented into the above describedscenario is that of an interface point associated with a node. Inmulti-layer networks, an interface can provide flexible connectivitybetween signal routing layers, as well as providing connectivity betweenan end of a link and a switch matrix in one or more signal routinglayers. Flexible connectivity within an interface can be represented bya connectivity block with interface points toward (A) client signalrouting layers, (B) server signal routing layers, (C) a switch matrix inthe current signal routing layer, and (D) link connections to a neighbornode. The multi-layer flexible connectivity provided by a transmitinterface, physical facility, and receive interface can be modeledschematically by representing the relationships between connectivityblocks operating at the various signal routing layers.

FIG. 9 shows a general connectivity block 90. Transmit directionconnectivity, from a switch matrix toward a link, has the followingpossibilities:

-   -   i) C-D: connectivity from a switch matrix to link in this signal        routing layer.    -   ii) C-Bi: connectivity from a switch matrix to a server signal        routing layer. Bi represents a particular server type and        adaptation type. There can be multiple server choices and        multiple adaptation choices for a given server.    -   iii) C-A: connectivity from a switch matrix to a termination of        this signal routing layer leading to a client signal routing        layer which would be identified, along with the adaptation type,        on the signal stack during route calculation.    -   iv) A-D: connectivity from an origination point to a link in        this signal routing layer. If used at other than the beginning        of a route calculation, the client signal type and adaptation        type would be present on the signal stack.    -   v) B-D: connectivity from a server signal routing layer to a        link in this signal routing layer.    -   vi) A-Bix: connectivity from an origination point for this        signal routing layer to a server signal routing layer in the        transmit direction. The ‘x’ indicates a transmit direction.    -   vii) B-Ax: connectivity from a server signal routing layer to a        termination point in this signal routing layer in the transmit        direction.    -   viii) C-C: connectivity from a switch matrix to the same switch        matrix in this signal routing layer. This can be used, for        example, for a service function in this signal routing layer        that creates a new or improved copy, or generation, of the        signal to be routed, e.g. a regenerator or retimer.    -   ix) Bi-Bjx: connectivity from a server signal routing layer to a        server signal routing layer in the transmit direction. The term        i may be the same as j in the case of a service function, as        above, or i and j may be different representing a change from        one server type to another or one adaptation type to another.

Receive direction connectivity, from a link toward a switch matrix, hasthe following possibilities:

-   -   i) D-C: connectivity from a link to a switch matrix in this        signal routing layer.    -   ii) D-A: connectivity from a link to a termination point in this        signal routing layer.    -   iii) D-Bi: connectivity from a link to a server signal routing        layer.    -   iv) A-C: connectivity from an origination point to a switch        matrix in this signal routing layer.    -   v) B-C: connectivity from a server signal routing layer to a        switch matrix in this signal routing layer.    -   vi) A-Bir: connectivity from an origination point in this signal        routing layer to a server signal routing layer in the receive        direction. The ‘r’ indicates a receive direction.    -   vii) B-Ar: connectivity from a server signal routing layer to a        termination point in this signal routing layer in the receive        direction.    -   viii) Bi-Bjr: connectivity from a server signal routing layer to        a server signal routing layer in the receive direction. The term        i may be the same as j for regeneration, or different for a        change in server type and/or adaptation type.

FIG. 10 shows an alternative Connectivity Attribute Group (CAG) 100. Asdiscussed previously, a CAG represents a connectivity block, a portionof the flexible connectivity provided by a link between an advertisingnode and a neighbor node. A link advertisement includes a list of CAGs,each of which represents flexible connectivity available within a givensignal routing layer and the cost and other attributes associated withthat connectivity.

The fields in CAG 100 are as follows:

-   -   i) Current Signal Type: identifies a type of signal routing        layer, in a link state advertisement all the signal routing        layers supported in the transmit direction on the advertising        node and in the receive direction on the neighbor node may be        specified (signal routing layers are not included if their        connectivity is fixed and thus of no interest in route        calculations). There may be more than one CAG with a given        Current Signal Type in an interface.    -   ii) CAG ID: identifies a CAG in the context of a link        advertisement. This ID must be unique within the scope of a link        advertisement.    -   iii) Connectivity Type: specifies one of the seventeen        connectivity types listed above, in a link state advertisement        the CAG includes transmit direction connectivity provided by the        advertising node and receive direction connectivity provided by        the neighbor node.    -   iv) Regeneration Flag: indicates whether or not the connectivity        includes regeneration, that is, whether a new generation of the        signal is created (this is noted in the route calculation as        each generation of a signal may visit a node only once in the        SPT).    -   v) Cost: the assigned cost of using this connectivity at this        signal routing layer in a route. Multiple cost values may be        provided for cases in which the cost policy can be selected or        affected by routing constraints.    -   vi) Available Capacity: the available capacity of this        connectivity at this point in the network. Capacity may be        expressed, for example, in bits per second or as a number of        predetermined resource partitions (e.g., number of timeslots or        channels). Multiple available capacity values may be provided if        resource state (e.g., operationally up, operationally down,        planned) and/or connection priority information is to be        considered in calculating routes.    -   vii) Next CAG ID: identifies the next CAG to examine following        connectivity to an A, B, or D point.    -   viii) Server Signal Type: indicates the server signal routing        layer to which this signal is adapted by this connectivity type.        This field applies to connectivity types toward B points.    -   ix) Adaptation Type: indicates the type of adaptation to the        server signal routing layer for this connectivity type. This        field applies to connectivity types toward B points.    -   x) Capacity Conversion: indicates how requested capacity at this        signal routing layer is converted to requested capacity at the        server signal routing layer specified by this connectivity type.        This field applies to connectivity types toward B points.    -   xi) Endpoint Affinity: identifies a list of router identifiers        that indicate which nodes should have preferential treatment for        termination of a server trail that originates at this node while        routing this signal type.

FIG. 11 shows an example of a Signal Stack 110. Signal Stack 110 carriesinformation about the layer network transitions that have occurredduring a route calculation. The fields in Signal Stack 110 are asfollows:

-   -   i) Signal Type: the type of the current signal routing layer        when this entry is at the top of the signal stack.    -   ii) Generation: the generation of the signal being routed in        this signal routing layer. Each generation of a signal may visit        a node only once in the SPT.    -   iii) Adaptation Type: the adaptation type used to adapt the        signal represented by this signal stack entry to the server        signal routing layer represented by the signal stack entry        immediately above, if any.    -   iv) Capacity Constraint: holds the capacity constraint for the        signal routing layer represented by this stack entry so that it        can be restored when the route calculation returns to this        signal routing layer.    -   v) Endpoint Affinity: a list of acceptable endpoints for popping        the signal stack entry immediately above this entry.

FIG. 12 is an example of a candidate entry 120 associated with acandidate node for placement into a candidate node list. During routecalculation, candidate route hops are maintained in a list ordered bycost. In the revised method there is additional information kept in thecandidate node list to allow holding candidates that represent partialtraversal of a link. The fields for candidate entry 120 are as follows:

-   -   i) Previous SPT Entry: the shortest path tree entry from which        this candidate is extended.    -   ii) Node ID: the identifier for the node within whose scope the        interface is identified.    -   iii) Interface ID: the identifier of the interface within whose        scope the CAG is identified.    -   iv) CAG ID: the identifier of the CAG to explore after this        candidate is placed in the SPT.    -   v) Interface Point Type: the type (A, B, C, or D) of the point        from which connectivity will be explored if this candidate is        extended.    -   vi) Working Signal Stack: the current value of the Signal Stack        for this candidate route hop.

FIGS. 13A-B show the example process of FIGS. 5A-B in determining aroute calculation using the advertised CAG information with changesshowing the interface point concept. The process shows how Dijkstra'salgorithm is changed to utilize the CAG information to accomplish routeextension via multiplexed and mapped server trails. Though changes toDijkstra's algorithm are shown, such changes are shown for examplepurposes only as the advertised CAG information may be implemented inother link state based route determination techniques and not limited toapplication to Dijkstra's algorithm. In the process shown, each node hasan associated node identifier and a signal stack to uniquely identifythe node. The signal stack is a stack of signal types that represent thecurrent layers for the connection being routed at this node. As with allstacks, new values are added or pushed on the top of the stack andvalues are removed or popped from the top of the stack.

The calculation performed by the process of FIGS. 13A-B yields a set ofintra-area routes associated with an area, Area A. A shortest path treeis determined by a node calculating the route using a specified node inthe network topology as a root. The formation of the shortest path treeis performed in two stages. In the first stage, only links between nodesin a single client layer are considered. In the second stage, linkswithin one or more server layers are considered. At each iteration ofthe algorithm, there is a list of candidate nodes. Paths from the rootto these candidate nodes have been determined but the shortest pathshave yet to be defined. Paths to the candidate node that is closest tothe root are guaranteed to be shortest. A path is said to be shorter ifit has a smaller link state cost. The link state cost of a path is thesum of the costs of the path's constituent links as they exist in alayer network (i.e., CAG). Upon identification, a candidate node isadded to the shortest path tree and removed from the candidate nodelist. Nodes adjacent to the candidate node added to the shortest pathtree are examined for possible addition to the candidate node list andthe shortest path tree. The algorithm continues to reiterate until thecandidate node list is empty.

In FIGS. 13A-B, process flow begins at block 1350 where the datastructures of the algorithm are initialized and candidate nodes arecleared. A shortest path tree is initialized by adding first a node, forexample node V, representing the root with a signal stack containing thesignal requested to be routed. Subsequently, the shortest path tree isupdated to include new nodes meeting the desired routing constraints.Area A's Transit Capability is set to False. At block 1351, adetermination is made as to whether the added node has an interfacepoint. If so, then the process skips to block 1362 where a new set ofneighbor nodes are generated. If there is no interface point associatedwith the added node, the link state advertisement of node V added to theshortest path tree is examined at block 1352. Each link described by thelink state advertisement provides signal types and costs to neighboringnodes. For each described link beginning at block 1354, if theattributes of the link between node V and a neighboring node, forexample node W, do not satisfy the routing constraints requested, theexamined link is skipped and the next link is examined. If routingconstraints are satisfied, process flow proceeds to block 1356 wherenode W's link state advertisement is examined. At block 1357, if thelink state advertisement for node W does not exist, has reached amaximum age, or does not include a link back to node V, then the nextlink in Node V's link state advertisement is analyzed. Otherwise,process flow proceeds to block 1358 for an analysis of each CAG in thelink. At block 1359, if the attributes of the CAG do not satisfy therouting constraints, the next CAG in the link is analyzed. If routingconstraints are satisfied here, process flow proceeds to block 1360where the signal type of the CAG is compared to the top of node V'ssignal stack. If there is no match, the next CAG in the link isexamined. If there is a match of the signal type, an interface point isgenerated for node V at block 1361 and then the next link in Node V'slink state advertisement is analyzed.

If node V already has an associated interface point or an interfacepoint has been generated for node V and all of its links have beenidentified, process flow proceeds to block 1362 where the connectiontypes of the CAG are examined in order to generate new candidate nodes.For C-D and D-C connectivity availability, an instance of node W isformed with the current signal stack to specify uniqueness from oneinstance of node W to another. The advertised cost of each instance isset to the transit cost for the CAG. For B-A and C-A connectivityavailability, if the signal stack for node V has more than one entry,any client signal type of the CAG matches the second signal type in thesignal stack of node V, and the adaptation type matches, then aninstance of node W is formed with the current signal stack excluding thetop element of the signal stack for uniqueness and the advertised costis set to the CAG adaptation cost for that client signal type. For A-Band C-B connectivity availability, an instance of node W is formed withthe current signal stack and for each server signal type in the CAG. Theadvertised cost is set to the CAG adaptation cost for each server signaltype. For each instance of node W generated, process flow proceeds toblock 1364 to determine if the newly generated instance of node W isalready on the shortest path tree. If so, move on to the next generatedinstance of node W. If not, process flow proceeds to block 1366 wherethe link state cost for the path from the root to node W is calculated.The link state cost is the sum of the link state cost of the shortestpath to node V and the advertised cost. At block 1368, if the link statecost is greater than or equal to the value that already appears for nodeW in the candidate node list, then the next CAG is examined. If the linkstate cost is less than the value that appears for node W on thecandidate node list or if node W does not yet appear on the candidatenode list, then an entry in the candidate node list for node W is set tothe calculated link state cost at block 1369 and the next generated nodeW is examined.

Once all generated node W's for each CAG for each link have beenexamined, process flow proceeds to block 1370 where a node in thecandidate node list that is closest to the root is chosen and added tothe shortest path tree. At block 1372, if the node added to the shortestpath tree has a link state advertisement indicating that the destinationis directly connected or reachable and the signal stack for the addednode contains one entry equal to the destination signal requested, thenthe calculation of the route is complete. The route is obtained bytracing back from this added node to the root of the shortest path tree.If the route is not complete, process flow returns to block 1352 toexamine the link state advertisement for the newly added node.

When determining a route of a sub-network connection for a signalthrough a network, it is desirable to traverse from a client layer,where the signal originates, to a server layer and return. However,while the destination node may be accessible through both client andserver layers, the destination node may not support the adaptationfunction needed to support the client signal on all of its interfaces atthe server layer. As a result, the route calculation develops a paththat uses an adaptation function to return the connection to theoriginating layer of the signal prior to completing the route. Thisbehavior is supported through the B-A and C-A connection type. Since thesink connection type has an associated signal type, it is possible torequire the B-A and C-A connection type match the type of signal beingrouted. In the case where a particular client signal type is notsupported on an interface, the constraint matching function willinvalidate the B-A and C-A connection as a candidate for completing thesignal routing. The route calculation will then continue to evaluateother candidates. This behavior is also preferable when the destinationnode for which a route is being calculated is not the terminating nodebut a border node which connects this route calculation domain toanother domain. A link can be identified as being a border by looking atthe advertisement type found in the supporting routing protocol.

When determining the route of a signal through telecommunicationsnetwork 10, adaptation functions advertised on a link become candidatesfor extending that route through a server layer. This candidate will beevaluated along with other candidates that are within the same layer asthe signal being routed. The cost of the adaptation function, oradaptation cost, becomes a determining factor as to when a server layerconnection will be necessary to complete the route for the signal. Theremay be times where it is desirable to control the points at which serverlayer extension will be allowed in route calculation. This does notchange the fact that an adaptation function exists and it is not removedfrom the advertisement described above. Instead, a special adaptationcost, such as 0xffff, can be used to denote that route extension througha server layer is prohibited for the signal.

FIG. 14 shows the change in block 1462 to the process of block 1362 inFIGS. 13A-B to implement this special adaptation cost. Since theadaptation cost is listed as part of the CAG associated with traversinga signal from a client layer to a server layer, the review of theadaptation cost occurs at the time that the adaptation is pushed ontothe signal path. The availability of the adaptation also is checked whentraversing from the server layer back to the client layer. Consequently,the return from server layer to client layer imposes a reverse check onthe availability of the client layer to server layer adaptationfunction. If the reverse check fails during the route calculation, thenthe return to the client layer cannot be accomplished at this point anda new candidate will then be evaluated. The check for the specialadaptation cost occurs during the generation of new candidate nodes.During the check for availability of a B-A, C-A, A-B, or C-Bconnectivity availability, if the adaptation cost has the specialadaptation cost value, in this case 0xffff, then a candidate node is notgenerated. If the adaptation cost is not the special adaptation costvalue, then a candidate node is added to the candidate node list.

FIG. 15 shows an example change in block 1562 to the process of block1362 in FIGS. 13A-B implementing an affinity cost adjustment for routeextensions via multiplexed server trails. When extending a route througha A-B and C-B connection followed by a server layer source connection, aspecial candidate route is created that has an added endpoint constraintthat it must reach a matching server layer B-A and C-A connection at anode that is already a neighbor of the current node for the linkcontaining transit connections at the client layer being routed. Thisspecial candidate route has its cost adjusted by reducing or eliminatingthe adaptation cost for the server layer. The endpoint constraint isapplied to this route candidate, and any route candidates that aregenerated from it, as the route calculation proceeds. The endpointconstraint for the special candidate route is determined by identifyingall the neighbors of the current node on links that support C-D and D-Cconnection types at the layer being routed regardless of whether or notthese links currently have C-D and D-C connections available. For theB-A and C-A connectivity check of block 62, the added limitation ongenerating a node W is that the top of the signal stack for node V haseither a NULL endpoint constraint or the endpoint constraint includesnode W. For the A-B and C-B connectivity check, a node W is generatedwith both an endpoint constraint and a NULL endpoint constraint. Theadvertised cost for the first generated node W is set to the CAG transitcost and the advertised cost for the second generated node W is set tothe CAG adaptation cost. The endpoint constraint is a list of affinityendpoints that can be used to terminate the server layer trail andachieve the costs associated with the path to node V. Any signal in thesignal stack, except the bottom signal, can be associated with a uniqueendpoint constraint. This method could be extended to create specialcandidate routes with different cost discounts depending on the numberand size of existing trunks to each current neighbor node.

There are various techniques that may be implemented for representingserver signal routing layer connectivity or potential connectivity inthe current signal routing layer topology. These techniques enable layerisolated signal connection routing and provide a client layer a view ofserver layer resources which may be used to satisfy a client layerdemand. That is, a signal connection may be routed in the current signalrouting layer without regard to details of adaptation to, orconnectivity in, server signal routing layers. The interface points ateach node allow a client layer network to request the establishment ofserver layer connections in order to complete a client layer connectionrequest. Before the connection can be requested, the client layer needsto determine the path that will be taken by the client layer connection.In order to use the server layer resources in the completion of theclient layer path, the server layer resources need to be represented insome manner in the client layer. It should be noted that, in some cases,to establish a signal connection using the route calculated in thecurrent signal routing layer, actions related to server signal routinglayers may be required. For example, adaptation types may have to beselected or provisioned, or server signal connections may have to berouted or established. In calculating routes in a server signal routinglayer network in support of signal connection in the current signalrouting layer, it may be necessary to include routing constraintsderived from those used to calculate the signal connection route in thecurrent signal routing layer. The various techniques for representingserver layer resources in the client layer include client layerSNPP-link connections using established server layer trails, clientlayer SNPP-link connections using potential server-layer trails, clientlayer pseudo node connections, and server layer topology shadowconnections in the client layer.

For client layer SNPP-link connections using established server layertrails, an established trail in a server signal routing layer provides alink in the current signal routing layer. For the lifetime of theestablished server layer trail, the link in the current signal routinglayer exists either (a) actually, if the related adaptation isprovisioned, or (b) potentially, if the related adaptation can be, buthas not yet been, provisioned. Note that a link in the current signalrouting layer may also be supported by multiple established server layertrails in series (a serial compound link).

In either case (a) or (b), a link can be advertised between the nodes atthe ends of the server layer trail with a CAG including C-D (transmit)connectivity on the advertising node and D-C (receive) connectivity onthe neighbor node. The available capacity should represent the selectednet capacity provided to the current signal routing layer by the servertrails supporting the link connection. The details of adaptation and theserver signal routing layer need not be advertised to enable layerisolated route calculation.

For client layer SNPP-link connections using potential server-layertrails, the endpoints of a potential link in the current signal routinglayer are identified, but the server trail supporting that link has notbeen established. Note that this case also applies to a series of trailssupporting the potential client layer link (serial compound link), atleast one of which has not been established. This technique extends uponthe technique above in that client layer SNPP links are allowed to begenerated for potential server layer trails before they are established.

The same link state advertisement as used in the technique where theserver trail is already established may be used in this technique aswell as the endpoints of the potential server trail are known.Additional operations are required in the server signal routing layer toestablish a server signal connection if this advertised link is used toestablish a signal connection in the current signal routing layer.However, this does not affect the layer isolated route calculation inthe current signal routing layer.

The management plane will specify a pair of access points that arepotentially connectable via a server layer and create potential SNPPlinks in the control plane for the supported client layers. Connectionsin the server-layer are not established until a request to use one ofthe potential client layer SNPP link connections is received by thecontrol plane. At this time, the client layer request is “suspended”while the server layer connections are established. Once theserver-layer connections are in-place, the client layer signaling isresumed. If a connection in the server layer cannot be established, thenthe client layer connection will also fail.

The specific path used for the server-layer connection may be calculatedin advance or at the time the connection is established. Ifcalculated/specified in advance, attributes of the server layer path(i.e. cost, SRLG, etc.) may be inherited by the client layer link.However, if it is calculated at the time of the server layer connection,then the attributes of the specific server layer path to be used areunknown. Consequently, the attribute information for the client layerSNPP link either needs to be specified by the management plane orderived from the aggregate potential paths between the identified pairof access points. Multiple client layer SNPP links between the sameaccess points may be used to deal with the case where multiple clientlayer paths exist with conflicting attributes.

If the specific server layer path is not calculated/specified inadvance, it is hard to identify if the server layer will have a pathavailable that meets the constraints specified by the client-layerconnection. If the specific server-layer path used to connect a pair ofaccess points is not calculated/specified in advance, a significantnumber of client layer SNPP links may be needed to uniquely identifyeach of the possible server-layer paths. Even if a single client layerSNPP link is created between each pair of potentially connectable accesspoints in the server layer, characterizing the complete amount ofconnectivity provided by the server-layer requires a full-mesh of clientlayer SNPP-links (one for each access point pair). Since the clientlayer SNPP link connections are created in advance of the server layertrail, the SNPP link connections are named independent of theserver-layer resources being used to support the client layer linkconnection, as the specific resource being used has not been identified.

For client layer pseudo node connections, a server signal routing layernetwork is projected into the current signal routing layer as a node,called a Pseudo Node, representing the possible connectivity provided bythe server layer to the current layer. The server layer and theadaptation are encapsulated to the client layer in a sub-network. Thisresults in the generation of something that looks like an abstract nodein the client layer representing the potential connectivity provided bythe server layer. However, unlike a normal abstract node, the SNPP linksinto the abstract node do not necessarily represent client layer links.Rather, they represent the client layer CP attached to the adaptationfunction which enters the server layer, and the TCP at the edge of theserver-layer subnetwork. It should be noted that this relationship notonly occurs between network elements, but sometimes occurs within anetwork element

To support layer isolated route calculation, a link to the pseudo nodeis advertised for each access point to the server signal routing layernetwork. Separate pseudo nodes are used for each distinct server layernetwork (set of connectable access points) and adaptation type. A pseudonode thus can be identified with a unique combination of server signaltype, adaptation type, and CAG ID. The link advertisement specifies C-Dconnectivity at the advertising node and D-C connectivity at theneighbor node (pseudo node).

It may not be desirable to require nodes that operate strictly in theserver signal routing layer network to participate directly in layerisolated routing for the current signal routing layer, so theadvertising router in the current signal routing layer may alsoadvertise the link from the pseudo node to itself. This link isadvertised from the pseudo node's point of view (the pseudo node isidentified as the advertising router) with C-D connectivity at thetransmitting end and D-C connectivity at the receiving end.

The pseudo node use a unique node ID identifying it in routingadvertisements. The value may be provisioned in the nodes advertisinglinks to the pseudo node or learned from nodes participating in theserver signal routing layer. Since points in the server signal routinglayer need not be explicitly identified in layer isolated routing, thepseudo node end of the advertised link is not required to have a uniqueidentifier in the context of the server signal routing layer network.For example, a null ID could be used. This requires routes calculatedvia a pseudo node link to identify the link end in the current signalrouting layer to eliminate ambiguity. The values of Server Signal Type,CAG ID, and Adaptation Type can be included in the optional fields ofthe link advertisement to allow this information to be included in thecalculated route, if desired.

As with the previous technique, the server layer connection isn'testablished until a request for a sub-network connection is made in theclient layer. This connection request is “suspended” while the serverlayer connection is signaled. Once the server layer connection isestablished, the client layer connection is resumed. Use of the serverlayer to complete a client layer connection can be controlled by settingthe cost of the link to the pseudo node. Unlike the previous technique,this approach scales linearly as access points are added to the serverlayer network. The pseudo node approach hides the detail of the serverlayer and therefore shares a number of the issues that affect abstractnodes, specifically non-optimal paths may be developed as the cost ofthe links in the server layer is not known and connections may beblocked due to a lack of available resources.

For server layer topology shadow connections in the client layer, aserver signal routing layer network is projected into the current signalrouting layer as a direct topology mapping, with available capacity onlinks adjusted as appropriate to represent the capacity (and possiblyallocation granularity) provided by the server signal routing layer tothe current signal routing layer. As in the pseudo node case, adifferent set of advertisements is provided for each unique serversignal routing layer network and adaptation type.

A transformation of a server signal routing layer network topology isadvertised in the current signal routing layer. This transformation maybe performed by one or more nodes participating in the server signalrouting layer, or by another entity with access to the server signalrouting layer network topology. All server layer links are advertised asthough they were present in the current signal routing layer, with theiravailable capacity adjusted according to the selected adaptation, andthe cost set according to operator policy regarding use of server signalrouting layer resources in support of current signal routing layerconnections.

For the shadow connections, the SNPP links and nodes viewed in theclient layer inherit attributes of the server layer SNPP links and nodesrespectively. The server layer link capacity viewed by the client layercan be interpreted in terms of client layer link capacity as, forexample, client layer SNPP link connections. However, the client layerneeds to understand the minimum allocation of link capacity possible onthe link in order to properly reflect the fact that creating a serverlayer connection to facilitate one client layer link connection mayactually busy out more than one client layer link connection ofcapacity. This information may then be provided as an input whenevaluating a link to determine if establishing a server layer connectionis acceptable. Providing the client layer path computation functionvisibility to the server layer topology has a number of benefits,including more optimal paths may be developed, as the cost of links inthe server layer is known, and being able to identify if capacity isavailable in the server layer.

A control plane instance for a layer network is not limited to using anyone of these techniques at a time. In fact, it makes sense to use morethan one of these approaches at the same time. For example, a topologymay start with a pseudo node showing the potential to connect clientlayer nodes. As server layer connections are established to serviceclient layer demands, client layer SNPP links are formed between theclient layer nodes. As the SNPP link connections which are a part ofthese links are released (i.e. transition from busy to available), theymay stay allocated to the client layer. Therefore the SNPP link betweenthe client layer nodes continues to be shown in the routing topology.

The example data structures used in the embodiment described have beenchosen to allow straightforward description of the route calculationalgorithm. More efficient encoding of the information may be possible.For example, more compact link state advertisements accompanied byadjustments on the algorithm to employ these encodings may be includedas an implementation.

In addition to cost, other cumulative metrics relevant to routecalculation can be included in a CAG Entry. For example, measures orestimates of loss or other signal degradation in analog networks can beincluded.

In summary, effective multi-layer network routing can be performedthrough advertisement of appropriate link state information and throughthe use of the link state information during route calculation. The linkstate information includes connection type attributes that specify notonly how a node can transport information in a layer and between layersof a network but also identify optimal points to move between layers andwhat nodes provide access to a desired layer of the network. Multi-layernetwork routing may also be represented in a layer isolated connectionrouting approach through the use of pseudo nodes.

The techniques performed by the present invention may be implemented insoftware, hardware, or a combination of both. For example, each node mayhave individual modules that can identify the different signal types andconnection routing layers associated with the node, determine theconnection types and availabilities corresponding to each connectionrouting layer at the node, and broadcast the link state advertisement,either in separate modules or different functions may be combined intothe same module. Modules may also be provided to calculate a routethrough the network and determine the various transit and adaptationcosts associated with connections in the network. These modules mayprovide the structure within the network for performing thefunctionality of the present invention.

Although the present invention has been described in detail withreference to particular embodiments, it should be understood thatvarious other changes, substitutions, and alterations may be made heretowithout departing from the spirit and scope of the present invention.For example, although the present invention has been described withreference to Dijkstra's algorithm, other routing calculations may beused with equal effectiveness in the present invention. Moreover, anumber of potentially suitable components that facilitate the processingof information in various types of formats, any suitable objects,elements, hardware, or software may be used in the applications oroperations described above. The arrangements described above inconjunction with telecommunications system 10 provide only an exampleconfiguration used for purposes of teaching and substitutions andmodifications may be made where appropriate and according to particularneeds.

Other changes, substitutions, variations, alterations, and modificationsmay be ascertained by those skilled in the art and it is intended thatthe present invention encompass all such changes, substitutions,variations, alterations, and modifications as falling within the spiritand scope of the appended claims. Moreover, the present invention is notintended to be limited in any way by any statement in the specificationthat is not otherwise reflected in the appended claims.

1. A method for multi-layer network routing, comprising: establishing aninterface point at each node of a network; determining signal typesimplemented at each node of the network, each signal type indicating aconnection routing layer in the network; determining connection typesthrough the interface point for each signal type and connection routinglayer at each node of a network at each link of each node; determiningavailability of each connection type; broadcasting signal types,connection types, and availability from each node to each neighboringnode in the network.
 2. The method of claim 1, further comprising:including limiting properties of each link associated with each node inthe connection type determination.
 3. The method of claim 1, furthercomprising: calculating a route from an originating node to adestination node through different connection routing layers of thenetwork.
 4. The method of claim 1, further comprising: establishing afirst adaptation cost at each node capable of providing a connectionfrom a first connection routing layer to a second connection routinglayer.
 5. The method of claim 4, further comprising: assigning aparticular value to the first adaptation cost in order to prevent theconnection from the first connection routing layer to the secondconnection routing layer.
 6. The method of claim 4, further comprising:establishing a second adaptation cost at each node capable of providinga connection from the second connection routing layer to the firstconnection routing layer.
 7. The method of claim 6, further comprising:assigning a particular value to the second adaptation cost in order toprevent the connection from the second connection routing layer to thefirst connection routing layer.
 8. The method of claim 1, furthercomprising: identifying nodes having preferential treatment fortermination of a connection routing layer.
 9. The method of claim 1,further comprising: assigning a transit cost associated with eachrouting layer supported by a connection from one node to another. 10.The method of claim 1, further comprising: providing information from aparticular node as to its capability to traverse from a first connectionrouting layer to a second connection routing layer and a capability of aneighbor node to traverse from the second connection routing layer tothe first connection routing layer.
 11. A network for communicatingtransport signals, comprising: a plurality of nodes, the plurality ofnodes operable to communicate transport signals over a plurality oflayers of the network, each layer representing a different transportsignal type where the originating layer is a client layer and the otherlayers are server layers, each node having an interface point associatedwith connections to and from the client layer and the server layers,each node operable to generate and broadcast a link state advertisement,the link state advertisement operable to indicate a connectioncapability of a particular node and a connection capability of aneighbor node to the particular node for each layer through therespective interface points, the link state advertisement operable todetermine through which layers in the network a transport signal can berouted.
 12. The network of claim 11, wherein the connection capabilityof the particular node and the neighbor node are provided in aconnection type field of the link state advertisement, the connectiontype field operable to indicate any of a transit, source, sink, danglingegress, dangling ingress, dangling source, and dangling sink connectiontypes associated with a link of the particular node.
 13. The network ofclaim 11, wherein the link state advertisement includes an availabilityand adaptation cost associated with traversing from one layercorresponding to another layer within the particular node.
 14. Thenetwork of claim 11, wherein the link state advertisement includes anavailability and an adaptation cost associated with traversing from aserver layer of the network to a client layer at the neighbor node. 15.The method of claim 11, wherein the link state advertisement includes alist of nodes in the network having priority for terminating a trail ina server layer.
 16. A computer readable medium including code formulti-layer network routing, the code operable to: establishing aninterface point at each node of a network; determine signal typesimplemented at each node of a network, each signal type indicating aconnection routing layer in the network; determine connection typesthrough the interface point for each signal type and connection routinglayer at each node of a network at each link of each node; determineavailability of each connection type; broadcast signal types, connectiontypes, and availability from each node to each neighboring node in thenetwork.
 17. The computer readable medium of claim 16, wherein the codeis further operable to: calculate a route from an originating node to adestination node through different connection routing layers of thenetwork.
 18. The computer readable medium of claim 16, wherein the codeis further operable to: determine cost values associated with traversingfrom one connection routing layer to another.
 19. The computer readablemedium of claim 16, wherein the code is further operable to: identify aconnection capability of a neighbor node; provide the connectioncapability of the neighbor node in the broadcast from a particular node.20. The computer readable medium of claim 16, wherein the code isfurther operable to: provide an indication to prevent traversing fromone connection routing layer to another at a particular node.